Caffeine is the most widely consumed stimulant. Caffeine is known to in-crease energetic metabolism throughout the brain, but it also decreases cerebral blood flow, inducing relative cerebral hypoperfusion. Caffeine ac-tivates norepinephrine neurons and appears to affect the local release of dopamine. Many of the warning effects of caffeine may be related to the action of methylxanthine on serotonin neurons. In this sense, this study aimed to identify the main effects of caffeine on the body. This is a literature review study addressing the main effects of caffeine on the body. In order to select the studies, an online survey of articles has been conducted on sites such as the Scientific Electronic Library Online (SciELO), Medical Literature Analysis and Retrieval System Online (MEDLINE) and Latin American and Caribbean Literature in Health Sciences (LILACS), using the descriptors “caffeine”, “effects of caffeine” and “methylxanthine”. We included the studies published between the years 2000 to 2018, which explicitly contemplate the evaluated aspects. In general, caffeine has effects on anxiety and sleep that vary according to individual sensitivity to methylxanthine. The central nervous system does not appear to develop a great tolerance to the effects of caffeine, although the symptoms of dependence and withdrawal are reported.